U.K. Summer 2007 Floods

, 2007 JuneU.K. Summer 25 2007 Floods 160 24 hour 20 July Monthly Average 140 25 June 120 100 15 June 80 Rainfall (mm) 60 40 20 0 Birmingham Hull Pershore 300% 250% e ag 200% aver 150% 2000 100% 1971- % % Jan Feb Mar Apr May Jun Jul Aug 50% 0% 2007 July 20TM , 2007 Risk Management Solutions Ic ACKNOWLEDGEMENTS Author Alice Stuart-Menteth Editor Shelly Ericksen Graphic designer Yaping Xie Contributors Claire Souch, Neena Saith, Ben Drinkwater, Robert Muir-Wood, Celine Herweijer, Dag Lohmann References 1947 U.K. River Floods: 60-year Retrospective. RMS, 2007 (www.rms.com) Association of British Insurers (www.abi.org.uk) Blackburn, M., B. Hoskins, and J. Slingo, 2007. Notes on the Meteorological Context of the U.K. Flooding in June and July 2007. Walker Institute publication, University of Reading, U.K. Chartered Institute of Loss Adjustors (www.cila.co.uk) Dealing with Flooding: A review of floods in North and North-West England January 2005. Environment Agency. Environment Agency (www.environment-agency.gov.uk) June 2007 Hydrological Summary for the United Kingdom, Center for Ecology & Hydrology (CEH) Trenberth K. E., P. D. Jones, 2007, IPCC WG1 AR4 Report, Chapter 3, 235–336. U.K. Meteorological Office (www.metoffice.gov.uk) Image Sources NOAA/ESRL Physical Sciences Division, Boulder Colorado (www.cdc.noaa.gov) Ic TaBLE OF CONTENTS EXECUTIVE SUMMARY 1 INTRODUCTION 2 THE SUMMER 2007 U.K. FLOOD EVENTS 4 June 25 Flood Event 4 July 20 Flood Event 5 THE CAUSE OF THE FLOODING 8 Antecedent Conditions 8 Summer Conditions 9 June rainfall 9 July rainfall 10 INSURED LOSSES 11 EVENT IN PERSPECTIVE 13 Hazard Perspective 13 Are the extreme rainfall events a product of climate change? 13 Does the abnormal rainfall this summer increase the risk of flooding this winter? 14 Market Perspective 14 EXECUTIVE SUMMARY The summer of 2007 has been the wettest summer in England and Wales since precipitation records began in 1766. During June, July, and August a succession of depressions tracked over the U.K., bringing heavy rainfall and triggering multiple flooding events. The floods ranged from small, localized flash floods to widespread events affecting major river basins. Two particularly large floods hit within just four weeks of each other. First, the northeast of England was badly affected following heavy rainfall on June 25, which caused flooding in cities and towns such as Sheffield, Doncaster, Rotherham, Louth, and Kingston-upon-Hull. Some areas were hit again by further flooding after more severe rains on July 20, which affected a much larger area of central England, including Oxford, Gloucester, Tewkesbury, Evesham, and Abingdon. These have been the most severe floods in 60 years since the March 1947 snowmelt floods, and the effects of the summer 2007 floods on some major rivers, such as the Lower Severn, have been comparable to the 1947 event. Figure 1: Flooding in Toll Bar, Yorkshire after June 25, 2007 rainfall event The summer floods have resulted in the largest flood insurance losses in the U.K. to date. As of September 2007, close to 60,000 claims have been reported and RMS estimates total insured losses to be in the range of £2.25–£3.25 billion from the two major flood events. Flood insurance was introduced into standard insurance policies in the U.K. in the 1960s, and while the summer 2007 floods were not as physically extensive as the 1947 flood, the two major summer 2007 flood events exceed the previous largest insurance flood loss, which was caused by the November 2000 floods. This report reviews the summer 2007 flooding events in the context of the key drivers of the flood and the losses together with the implications for the insurance market and catastrophe flood risk modeling. INTRODUCTION The floods of summer 2007 were linked to a pattern (Figure 3). Table 1 presents a time series of the of very wet and unstable weather across the U.K. over summer flood events, of which this report focuses on the course of several months. The unseasonably wet the two biggest and most devastating events — the weather began in May and continued throughout the June 25 and July 20 floods. summer, with record-breaking rainfall totals in June This report discusses the characteristics, drivers and July. Exceptionally intense rainfall events caused and impacts of the summer 2007 flooding events. At severe flash flooding in many areas across the U.K. the time this report was published (mid-September and, as catchments became saturated, swollen rivers 2007), the insurance market, the Environment Agency, overtopped their banks in several major river basins. and other government bodies were still evaluating Intense heavy rainfall is not unusual during the the full extent and impact of the floods. This report, summer, but in 2007 the frequency and spatial extent which summarizes the damage and cause of these was unprecedented. During this period, there were major flood events, is based on the information two exceptional rainfall events on June 25 and July available at the time. 20 that caused widespread flooding across England During the summer floods, RMS sent out several Date of Locations Flooded Flash Major River Event(s) Flooding Flooding June 1–7 Buckinghamshire (E) √ June 8–14 Lancashire (E); Northern Ireland, Ceredigion (W) √ June 15–21 County Durham, Devon, Herefordshire, North √ √ and West Yorkshire, Shropshire, Worcestershire (E); Ards, Down, North Down (NI); Ayrshire, Lanarkshire (S); Ceredigion (W) June 22–28 Yorkshire, Lincolnshire, Humberside, Derbyshire, √ √ Nottinghamshire, Shropshire, Worcestershire (E); Peeblesshire (S); Denbighshire, Flintshire, Monmouthshire, Wrexham (W) June 29 – Buckinghamshire, Lancashire, West Yorkshire (E); √ July 5 Antrim (NI); Midlothian, Moray (S) July 13–19 County Durham, Cumbria, Lancashire, North √ Yorkshire, Worcestershire (E); Coleraine, Larne (NI); Ayrshire, Dumfriesshire, Ross and Cromatry (S); Denbighshire (W) July 20–26 Bedfordshire, Berkshire, Buckinghamshire, √ √ Cambridgeshire, Dorset, Gloucestershire, Greater London, Hampshire, Herefordshire, Hertfordshire, Lincolnshire, Northamptonshire, Oxfordshire, Shropshire, Warwickshire, West Midlands, Wiltshire, Worcestershire (E); Newport, Monmouthshire, Powys, Torfaen, Glamorgan (W) August 20–21 Devon, Kent √ Table 1. Summary of 2007 June–August Floods (E: England, NI: Northern Ireland, S: Scotland, W: Wales) 2 Figure 2: Flooding observed in Tewkesbury during RMS reconnaissance surveys Main Affected Rivers reconnaissance teams to survey the damaged areas 25 June Flood Event and speak to residents and businesses about their 20 July Flood Event experience. The teams, which included seven flood and vulnerability specialists, visited Doncaster, Sheffield, Barnsley, Catcliffe, Tewkesbury, Evesham, Oxford, Abingdon and Pangbourne. Information gathered from the reconnaissance surveys has been used throughout this report, in particular to inform the assumptions when deriving loss estimates for the ! Leeds Hull ! events which are discussed within the report. ! Doncaster ! ! Sheffield Louth Birmingham ! ! Worcester Gloucester ! !Oxford ! ! London Reading Figure 3: Flooded postcode sectors from June 25 (blue) and July 20 (purple) flood events collated by RMS Catastrophe Response, from a combination of RMS field reconnaissance, media reports, and other Web0 reconnaissance15 30 60 information. 90 120 Kilometers Each whole postcode sector is unlikely to have flooded everywhere, especially in rural areas, where postcode sectors cover a larger area 3 THE SUMMER 2007 U.K. FLOOD EVENTS The two severe rainstorms of June and July caused overflowed in Leeds, flooding just over 100 properties. widespread fluvial and flash flooding across England and The city escaped catastrophe by millimeters as the flood parts of Wales (Figure 3). In both events, the flooding waters continued to rise on Monday. The River Don in had distinct phases: flash flooding with surface runoff, Sheffield burst its banks, flooding properties, including and extremely high flows in small responsive catchments the many commercial and industrial units that lie along followed by extensive floodplain inundation as the runoff the river. During Monday night, the River Rother, to the concentrated along the major river basins. These two south of Sheffield, overtopped its banks, flooding around events are discussed in more detail in this section. 100 properties in the flood-prone village of Catcliffe. Flash flooding is defined as the result of heavy or Flood depths were so high that bungalows were almost excessive amounts of rainfall within a short period of completely submerged by the flood water. The flood time, usually less than six hours, causing water to rise wave continued, traveling down the River Don and its and fall rapidly. It includes sources of flooding from small tributaries from Sheffield through Rotherham toward rivers with rapid response times to rainfall, together with Doncaster. On Wednesday night the River Don and its overland flow, which in the majority of cases is caused tributaries overflowed in and around Doncaster, severely by the rainwater exceeding the infiltration capacity of flooding areas in the North of the city. Table 2 lists the the ground. This is of particular concern in urbanized number of flooded properties reported in some of the landscapes, were there is little capacity for the ground to worst affected towns and cities (Figure 4). absorb rainfall due to the built environment. The highest In most cases, flood waters quickly receded, except standard for surface water

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